Tonalite

Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic (coarse-grained) texture.

Quartz (SiO2) is present as more than 20% of the total quartz-alkali feldspar-plagioclase-feldspathoid (QAPF) content of the rock.

[1][2] Amphiboles and biotite are common in lesser quantities, while accessory minerals include apatite, magnetite and zircon.

[6] Trondhjemite is an orthoclase-deficient variety of sodium-rich tonalite with minor biotite as the only mafic mineral, named after Norway's third largest city, Trondheim.

[7] Tonalites, together with granodiorites, are characteristic of calc-alkaline batholiths formed above subduction zones.